Stock-Based Compensation - Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Employee and non-employee stock options
Stock based compensation expense
Options granted (in shares)			390,000
Stock-based compensation expense	$ 35,103	$ 11,957	$ 58,335	$ 19,374
Unrecognized compensation expense	207,400		$ 207,400
Unrecognized compensation expense, weighted average period of recognition			2 years 9 months 18 days
Employee and non-employee stock options | Cost of revenues
Stock based compensation expense
Stock-based compensation expense	1,275	441	$ 1,983	755
Employee and non-employee stock options | Research and development
Stock based compensation expense
Stock-based compensation expense	6,616	2,913	10,490	4,755
Employee and non-employee stock options | Selling, general and administrative
Stock based compensation expense
Stock-based compensation expense	27,212	8,603	45,862	13,864
Employee stock options
Stock based compensation expense
Stock-based compensation expense	34,697	11,599	57,660	18,847
Employee stock options | Cost of revenues
Stock based compensation expense
Stock-based compensation expense	1,275	441	1,983	755
Employee stock options | Research and development
Stock based compensation expense
Stock-based compensation expense	6,276	2,631	9,926	4,313
Employee stock options | Selling, general and administrative
Stock based compensation expense
Stock-based compensation expense	$ 27,146	8,527	$ 45,751	13,779
Non-employee stock options
Stock based compensation expense
Options granted (in shares)			32,053
Options unvested (in shares)	2,188		2,188
Stock-based compensation expense	$ 406	358	$ 675	527
Non-employee stock options | Research and development
Stock based compensation expense
Stock-based compensation expense	340	282	564	442
Non-employee stock options | Selling, general and administrative
Stock based compensation expense
Stock-based compensation expense	$ 66	$ 76	$ 111	$ 85